In the control of fluid in industrial processes, such as oil and gas pipeline systems, chemical processes, etc., it is often necessary to reduce the pressure of a fluid. Adjustable flow restriction devices such as flow control valves and fluid regulators and other fixed fluid restriction devices such as diffusers, silencers, and other back pressure devices are utilized for this task. The purpose of the fluid control valve and/or other fluid restricting device in a given application may be to control flow rate or other process variables, but the restriction induces a pressure reduction inherently as a by-product of its flow control function.
Currently there is available an assembly of a plurality of stacked disks forming a fluid pressure reduction device fused together in a brazing process with additional mechanical fasteners added if desired to securely maintain the stacked disks assembled. As an example, in U.S. Pat. No. 6,026,859, assigned to the same assignee as herein, a plurality of stacked disks include alternating flow disks and plenum disks. Respective cage ends are provided on opposite ends of the stacked disks. One of the cage ends includes a series of threaded bores and the opposite cage end includes a corresponding number of countersunk bores. A corresponding number of holes are drilled, cut or punched through each disk so that in the assembled stacked disks configuration, each disk hole can be aligned with a respective threaded bore in one cage end and with a respective countersunk bore in the opposite cage end. In the final assembly, a threaded bolt is inserted through the one cage end and through the disks to threadably engage the threaded bore in the opposite cage end.
In the manufacturing process for this stacked disk assembly, each individual disk and the cage ends are coated with a nickel plating. The nickel plated disks and the cage ends are assembled into a stack which is placed in a fixture and subjected to a suitable temperature in an oven during a brazing process to fuse the individual plated disks to each other as well as to the opposite cage ends.
Problems have been encountered in thereafter attempting to threadably engage the threaded bolt with the threaded bore in the cage end due to the nickel in the brazing process being deposited into the threads of the threaded bore. Various attempts have been made to prevent the nickel from being deposited onto the threads in the cage end threaded bores, all of which attempts have met with limited success. Thus, despite various efforts the final assembly problem in trying to provide a mechanical fastening of the stacked disks still exits.
Other problems encountered are due for instance to distortion in the threads caused by the high temperatures in the brazing oven. Thread distortion may cause increased difficulty in assembly, overtorqueing of the threaded bolt, and insufficient bolt load.
In accordance of the principles of the present invention, there is provided a stacked disk configuration and a process for assembling the stacked disks so that the stacked disks are not only fused together in the desired brazing process, but are also mechanically fastened together with threaded bolts to securely and reliably maintain the stacked disks assembled.
In the present invention, one cage end mounting member is provided with a series of inwardly converging, tapered bores and the other cage end mounting member is provided with a corresponding number of conventional countersunk bores. The disks and the cage end mounting members are nickel plated, subjected to a brazing process as in the prior process to fuse the disks and the cage ends to each other. A taper nut having internal threads and an external tapered surface with a taper angle which matches the inwardly converging tapered bore of the cage end mounting member is then inserted into each of the tapered bores.
A threaded bolt is inserted in each of the countersunk bores, and through corresponding aligned holes in each disk to threadably engage the taper nut. Continued threadable engagement of the bolt and the taper nut tends to pull the taper nut deeper into each inwardly converging, tapered bore and is continued until the desired torque amount is achieved. The taper nut is thereby self-locked in the tapered bore so that even if the threaded bolt is disengaged from the nut, the taper nut remains in the tapered bore.
The present invention thereby provides a unique taper nut retention device to mechanically fasten the stacked disks. Also, the present invention provides an improved process for assembling and mechanically fastening a plurality of fluid pressure reduction disks.
The present invention also may be utilized where the mounting members are of a material which is difficult to tap or otherwise form threads. Also, where the fastener cannot be allowed to extend beyond the outer dimensions of the mounting members, or where there are tight dimensions and a wrench can""t be used on a normal nut, a tapered bore in one mounting member can be formed and a taper nut dropped into the tapered bore.
A shallow taper angle of less than 30 degrees, and most preferably about five degrees is preferred, particularly so that the self-locking feature can be readily attained between the taper nut and the tapered bore of the mounting member. A significant advantage of the taper nut feature of this invention is that no welding of the nut is required to keep the nut in place during initial threadable engagement of the bolt or when the bolt is disengaged from the taper nut.